Typically, a printing press will utilize two printing couples and will have an inking mechanism for each of the two printing couples. The printing couples comprise a pair of plate cylinders that are commonly journaled at their opposite ends in spaced parallel side frames as well as a corresponding pair of blanket cylinders that are similarly journaled in the side frames. Further, the printing press will be formed to have a throw-off mechanism usually based on a system of eccentric sleeves and associated linkages.
For a printing press of this type, the press will commonly be designed to utilize a specific diameter of plate and blanket cylinders. It will be understood that the diameter of the cylinders dictates the printed image cutoff which has been difficult to vary since it has involved entirely changing the printing press components by essentially rebuilding the press. Understandably, this is a very costly operation to perform, and it is undesirable from the standpoint of productivity and use of resources.
In other words, there is a great amount of "down time" when it is desired to change the cutoff in a conventional printing press. To achieve this objective, it is also necessary to have multiple different sized components including various diameters of plate and blanket cylinders along with different gears, bearings and the like in order to be able to rebuild the press to achieve a different printed image cutoff. As a result, the cost of changing the cutoff has been a deterrent to achieving the level of flexibility that is desired in a printing press.
In an attempt to overcome these problems, Riggs et al. U.S. Pat. No. 2,447,872 suggested a manner of adapting a press for print and blanket cylinders of different diameters. It taught that substantially the same drive elements could be used throughout in constructing a press having cylinders of any one of a variety of diameters, provided appropriate alterations were made in the size of spur gears connecting the components of the printing couples. While eliminating the need for completely different sets of press drive parts, the Riggs et al. '872 patent failed to overcome all of the problems that had been encountered in the art.
By way of further background, Hannon U.S. Pat. No. 5,337,664 also discloses a printing press of the type that utilizes two printing couples. This patent utilizes a pair of blanket cylinders which are movably mounted by a throw-off apparatus to enable separation of the blanket cylinders from each other and from a corresponding pair of plate cylinders. As described therein, a pair of blanket cylinders are typically mounted for movement by means of a throw-off apparatus for separation to create a throw-off gap.
As will be appreciated by those skilled in the art, the throw-off gaps are needed to install and remove plates and blankets from the plate and blanket cylinders. The apparatus utilized for this purpose has conventionally employed a suitable linkage which is pivotally connected to a peripheral arm of an eccentric member to which a shaft of the blanket cylinders is typically mounted. For mounting or dismounting the plates and blankets, the linkage is moved by a conventional drive to turn the eccentric members from an operative to an inoperative position.
While such throw-off apparatus are well known, the same cannot be said for an apparatus for varying printed image cutoff. It would, thus, be highly desirable to have suitable means for mounting and dismounting plates on plate cylinders and blanket sleeves on blanket cylinders where the blanket sleeves have different thicknesses and, thus, different outer diameters to provide desired printing cutoff points. Moreover, to be advantageous, this should be achieved in a manner that does not require the press to be changed to any significant extent.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.